1. Field of the Invention
The present invention relates to an imaging lens and an imaging apparatus using the imaging lens.
2. Description of the Related Art
Mobile phones have been proposed which include imaging apparatuses each having an imaging lens and an imaging device that converts an optical image formed by the imaging lens into electric signals. The imaging apparatus is mounted on a printed circuit board provided in the mobile phone. In addition, a reflow mounting method has been known as a method of mounting the imaging apparatus on the printed circuit board. In the reflow mounting method, solder balls are arranged on the printed circuit board at positions where the imaging apparatus is mounted in advance, the imaging apparatus is arranged on the solder balls, and the imaging apparatus is heated to melt the solder balls and then cooled down. In this way, the imaging apparatus is soldered to the printed circuit board.
The imaging lens provided in the imaging apparatus mounted by the reflow mounting method needs to have heat resistance. Therefore, an imaging lens having a structure that is different from that of the imaging lens used in a normal environment has been examined.
For example, as an imaging lens that has heat resistance and can be mounted by the reflow mounting method, an imaging lens has been proposed which includes three lens groups each having a cemented lens obtained by bonding glass and a resin having heat resistance to be integrated with each other (see Japanese Patent No. 3946245 and JP-T-2005-539276 (corresponding to WO-A-2004/027880)). The imaging lens having three lens groups is used to form the optical image of a subject on a light receiving surface of an imaging device having, for example, two mega pixels each having a size of about 5 μm×5 μm.
However, there is a demand for a high-quality camera provided in a mobile phone. Specifically, there is a demand for a high-performance imaging lens applicable to an imaging device having a light receiving surface including two mega pixels or more. For example, there is a demand for the reflow mounting of an imaging apparatus, which is a combination of an imaging device having a light receiving surface including five mega pixels, each having a size of about 2 μm×2 μm, and a high-performance imaging lens having a high resolution corresponding to the imaging device, on a printed circuit board.
However, in the imaging lens including three lens groups, each having the cemented lens with heat resistance that is obtained by bonding the glass and the resin to be integrated with each other, it is difficult to further improve the optical performance thereof.
The above-mention problems arise in the imaging lens of the imaging apparatus mounted on the printed circuit board by the reflow mounting method as well as the imaging lens provided in the mobile phone.